The present invention relates to how to control a write current in a magnetic disk drive.
In recent years, magnetic disk drives including hard disk drives are used not only in computers, but also in hard disk recorders, portable music players, car navigation systems, and the like. Thus, the use of magnetic disk drives is expanding. Following this tendency, content handled by the magnetic disk drives is not limited to textual information. In recent years, the content covers music, images, video, and the like.
As shown in FIG. 6, for example, a magnetic disk drive comprises: a plurality of magnetic disks 400, each of which has a non-magnetic disk such as glass on which a magnetic layer is laminated; and a plurality of magnetic heads 401. Each of the magnetic heads 401 includes a write head for writing data to each magnetic disk 400, and a read head for reading data from said each magnetic disk 400. The plurality of magnetic disks 400 are mounted to one spindle 402. The plurality of magnetic heads 401, the number of which is the same as the number of surfaces of the magnetic disks 400, are mounted to arms 403. The arms 403 are pivotally moved by a voice coil motor (hereinafter referred to as “VCM”) 404. When write processing of writing data to the magnetic disk 400 or read processing of reading data from the magnetic disk 400 is performed, the magnetic head 401 is moved to a position that faces a surface of the magnetic disk 400. When both of the write processing and the read processing are not performed, the magnetic head 401 is unloaded from the surface of the magnetic disk 400.
In such a magnetic disk drive, data is written to an area that is concentrically located on the magnetic disk 400; or data is read out from the area. This area is called a track.
FIG. 7 is a diagram illustrating an example of tracks 501 located on a magnetic disk 500. As shown in FIG. 7, a plurality of tracks 501 are concentrically located at constant intervals (track pitch T). Each of the tracks 501 includes servo areas S and data areas D. The servo areas S are used to write information that is used when a magnetic head (not illustrated) is positioned at the time of read/write processing. The data areas D are used to write user data such as music data. It is to be noted that this data area D can be divided into the smallest units that can be accessed by the magnetic head. These units are called sectors.
It is demanded to increase the capacity of the magnetic disk 500 without sacrificing the miniaturization of the magnetic disk drive as a whole. In order to meet the demand, the recording density is improved, for example, by increasing the density (linear recording density) of data that is written in the circumferential direction of the tracks 501 located on the magnetic disk 500, or by reducing the width of each of the tracks 501 to narrow the track pitch T so that the track density is increased.
FIG. 8 is a diagram partially illustrating a structure of a write head. In this write head, by applying an electric current to a coil 600, a magnetic field is generated between a surface of an upper magnetic pole piece 601 that faces a magnetic disk surface (hereinafter referred to as “air bearing surface 602”) and a lower magnetic pole piece 603. The magnetic field causes the magnetic disk surface to be magnetized, with the result that data is written there. In order to narrow the track width so that the recording density is improved as described above, for example, it is necessary to narrow the tip of the write head. However, if the tip of the write head becomes narrower and narrower, the tip is saturated with magnetic flux. Accordingly, a phenomenon will occur in which a magnetic field leaks out not only from the air bearing surface 602 of the upper magnetic pole piece 601 but also from the side 604 of the upper magnetic pole piece 601. For this reason, if the track pitch is narrow, a leakage field from this side 604 extends over adjacent tracks that are located on both sides of a target track to which data is written. This leakage field from the side 604 is feeble in comparison with a write magnetic field that is generated between the air bearing surface 602 and the lower magnetic pole piece 603 so as to write data to a target track. The leakage field in question, therefore, does not immediately exert an influence upon data in the adjacent tracks. However, the data in the adjacent tracks is gradually erased if the leakage field repeatedly extends over the adjacent tracks multiple times. As a result, a phenomenon occurs eventually in which the data cannot be read out. This phenomenon is called ATI (Adjacent Track Interference).
With the object of solving the problem of ATI, for example, taking into consideration a change in temperature of a magnetic disk drive, a write-current value was heretofore determined (for example, see patent document 1 (Japanese Patent Laid-open No. 10-312504)).
However, as described above, fields and applications in which magnetic disk drives are made use of are expanded. For example, even if the same magnetic disk drive is used, a possibility of the occurrence of ATI may change to a large extent depending on how the magnetic disk drive is used by end users.
To be more specific, for example, if an end user uses a magnetic disk drive as a large-capacity storage medium for a music player, once music data is written to the magnetic disk drive, what is performed is mainly reading of the music data. Since the number of times data is written is small, therefore, the problem of ATI hardly occurs.
On the other hand, for example, if the end user uses the magnetic disk drive as a storage medium to which image data as a photograph taken by a digital camera is temporarily written, image data is frequently written or erased. Accordingly, the problem of ATI is liable to occur.
The conventional magnetic disk drives described above could not sufficiently prevent such ATI encountered depending on how the magnetic disk drive was used by the end user, in some cases.